Image forming apparatus having position detection mechanism

Abstract

In an image forming apparatus having a recording head including a plurality of nozzle arrays for ejecting each ink droplet per color for plural colors respectively onto a transported recording medium, a positioning mechanism of the image forming apparatus having a detection mechanism for preventing a printing quality on a recording medium from degrading by comprising a transport mechanism for transporting in order to form an image on the recording medium, and a carriage placed on an opposite positions of the transport mechanism and a belt platen; placing a sensor for detecting a relative inclination between the transport direction and the recording head; detecting and calculating an inclination of the transport direction vis-à-vis the recording head, and controlling the relative inclination based on the calculation result.

1. An image forming apparatus comprising:
 a recording head including a plurality of nozzle arrays for ejecting each ink droplet per color for plural colors respectively in a first direction onto a transported recording medium; 
 a transport mechanism for transporting the recording medium in a second direction in order to form an image thereon; 
 wherein the nozzle arrays are placed in a predetermined interval, and in a position opposite to the transport mechanism; 
 an inclination detection unit comprising a sensor for outputting a signal in order to generate information about a relative inclination between the second direction or the transport mechanism and the recording head around an axis that is perpendicular to the recording medium; and 
 a correction unit for calculating based on the signal and correcting a relative inclination between the second direction and the recording head based on the calculation result; 
 wherein said correction unit has a control unit for generating ejection information based on image information for inputting into said recording head, and the control unit generates ejection information by displacing in a nozzle row direction by a predetermined amount based on said signal; and 
 wherein said predetermined amount is calculated from a reference position, a distance between a reference position and a nozzle row and said signal. 
 
     
     
       2. The image forming apparatus according to  claim 1 , wherein said sensor outputs a signal for detecting a relative inclination between a belt which transports said recording medium and said recording heads around said axis. 
     
     
       3. The image forming apparatus according to  claim 1  wherein said sensor outputs a signal for detecting a relative inclination between a belt platen, on which a belt for transporting said recording medium is placed, and said recording heads around said axis. 
     
     
       4. The image forming apparatus according to  claim 1 , wherein said sensor at least comprises a light source and a light receiving element for receiving light emitted from the light source. 
     
     
       5. The image forming apparatus according to  claim 4 , wherein light emitted from said light source is incident on said light receiving element by way of a target, and both the light source and the light receiving element are placed on one of said recording heads or said transport mechanism, and the target is placed on the other one of said recording heads or said transport mechanism. 
     
     
       6. The image forming apparatus according to  claim 5 , wherein said target is placed on an entire circumference of said belt. 
     
     
       7. The image forming apparatus according to  claim 1 , wherein said sensor at least comprises a magnetic member and a magnetic sensor for detecting a magnetism of the magnetic member. 
     
     
       8. The image forming apparatus according to  claim 1 , wherein said sensor is a velocity sensor for detecting a velocity of said recording medium and/or a belt which transports the recording medium. 
     
     
       9. The image forming apparatus according to  claim 8 , wherein said velocity sensor is an optical velocity sensor. 
     
     
       10. The image forming apparatus according to  claim 9 , wherein said optical velocity sensor comprises means for a changeover control of a light path of emitted light of the optical velocity sensor, thereby detecting a velocity from two directions by a time sharing. 
     
     
       11. The image forming apparatus according to  claim 1 , wherein said inclination detection unit comprises two sets of sensors which are placed separately from each other in a vertical direction vis-a-vis said first direction. 
     
     
       12. The image forming apparatus according to  claim 1 , wherein said transport mechanism has a belt platen.